UNIVERSITY   OF    CALIFORNIA 

COLLEGE   OF   AGRICULTURE 

AGRICULTURAL    EXPERIMENT    STATION 

BERKELEY,  CALIFORNIA 

CIRCULAR  295 

September,  1925 

THE  GROWING  AND  HANDLING  OF 
HEAD  LETTUCE  IN  CALIFORNIA 

H.  A.  JONES  and  E.  L.  GAETHWAITE 


FOREWORD 

Within  the  past  few  years  there  has  been  a  very  great  increase  in 
the  production  and  consumption  of  lettuce  in  the  United  States.  This 
increase  in  consumption  has  followed  closely  the  introduction  of  the 
variety  of  head  lettuce  known  as  New  York,  which  in  the  United 
States  is  grown  only  in  the  western  irrigated  regions.  The  greatest 
increase  in  production  has  been  in  California  and  other  Pacific  Coast 
and  Rocky  Mountain  states  where  the  crop  is  grown  almost  entirely 
under  irrigation.  Fig.  1  shows  the  great  increase  in  carlot  shipments 
of  lettuce  in  the  United  States  and  in  California  since  1917.  Most 
of  the  lettuce  produced  near  the  large  cities  and  consuming  centers  in 
New  Jersey,  New  York,  and  other  states  is  hauled  to  market  by  truck 
and  therefore  does  not  appear  in  these  carlot  totals.  In  1923,  over 
40  per  cent  of  all  carlot  movements  in  the  United  States  originated  in 
California  and  in  1924  nearly  60  per  cent. 


PRODUCTION  AREAS  OF  THE  UNITED  STATES 

The  New  York  variety  is  produced  in  the  irrigated  regions  of  the 
West,  including  Arizona,  California,  Colorado,  Idaho,  Oregon,  Utah, 
and  Washington.  Big  Boston  is  grown  in  the  Middle  West,  East  and 
South,  particularly  in  Florida,  Michigan,  New  Jersey,  North  Caro- 
lina, South  Carolina,  and  Texas.  Attempts  have  been  made  to  grow 
the  variety  New  York  in  the  East,  but  the  heads  do  not  become  so 
firm  nor  the  quality  so  good  as  when  raised  under  Western  condi- 
tions. 


Z  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

Shipping  Seasons  of  Different  States. — Fig.  2  gives  the  approxi- 
mate lettuce-shipping  seasons  for  the  important  lettuce-producing 
states  and  districts.  The  shipping  season  of  each  locality  varies 
slightly  from  year  to  year  with  seasonal  conditions. 

Carlot  Movements  from  Different  States. — As  California  ships  let- 
tuce throughout  the  year,  it  must  compete  to  a  certain  extent  with 
lettuce  shipped  by  all  other  states.  Table  1  shows  the  carlot  movements 
for  the  entire  United  States  by  months  for  the  years  1918  to  1924, 
inclusive. 


bar- 
loads 

Cnrlnt   ShinmenTs  of  Letfur.p,  fnr  Unitfifl  Stntfif,  iqn-na* 

fihade.r 

Pnrl 

inr 

i  fiolrfnrnin   Shin  merits 

30000 

£8000 

£b000 

£4000 

££000 

£0000 

18000 

IbOOO 

14000 

l£000 

10000 

8000 

bOOO 

4000 

£000 

1917 

\Q\8 

WW 

igzo 

m\ 

i 

\m 

mi 

mA 

■ 

I  i 

|  | 

■  in 

I  I 

III  i 

n 

ill  II 

b 

u 

■ 

z 

■ 

z 

■  ■■II 
1  I  I  I  I 

Fig.   1.— Carlot  shipments  of  lettuce  for  United  States   1917-1924. 
Shaded  portion,  California  shipments. 


Carlot  Shipments  of 

TABLE  I 

Lettuce  for  the  United 

States  bt 

Months, 

1918- 

-1924 

Years 

Jan. 

Feb. 

Mar. 

Apr. 

May 

June 

July 

Aug. 

Sept. 

Oct. 

Nov. 

Dec. 

Total 

1918 

957 
767 
2023 
2356 
2245 
3119 
3807 

1124 
717 
1621 
1984 
1919 
2736 
3626 

1167 
829 
1353 
2219 
2584 
4099 
2789 

725 
1090 
1063 
1974 
3167 
2520 
2885 

499 
831 
1172 
1067 
1859 
2015 
3087 

92 
181 
365 
670 
801 
1310 
1261 

382 
395 
980 
1399 
1536 
2232 
1715 

560 
695 
934 
1140 
1787 
2493 
2053 

383 
653 
832 
1302 
1303 
1839 
1821 

123 
358 
596 
1253 
1503 
2048 
2145 

319 
565 
1388 
1481 
1453 
2285 
2762 

628 
937 
1491 
1771 
2083 
2789 
2840 

6959 

1919 

8018 

1920 

13818 

1921 

18616 

1922 

22240 

1923 

29485 

1924* 

30791 

Bureau  of  Agricultural  Economics. 


Subject  to  revision. 


ShiDpLnq 

Distr 


LSiXIC 


Is. 


Rnzono 


California  N.P 


California  S.P 


California 


CJDl 


r 


/ali  forma LSL 


Colorado 


-tnrida 


dahn 


Michi 


qan 
Minnesota 


NfiurJfirsfiij 


W  Mexico 


New  York 


North  Carolina 


Q 


DHL 


Q 


reoon 


% 


Soulb  rami  inn 


£Xi2_S 


Virginia 


Wash 


inplnn 


9 


v-qq  rnrlnnd.^ 


Tmifin-iqqr.nrlnQd.s 


Fig.  2. — Shipping  districts.     Approximate  shipping  season,  1924. 


UNIVERSITY    OF    CALIFORNIA — EXPERIMENT    STATION 


PEODUCTION   AKEAS    IN    CALIFOBNIA 

The  main  lettuce-producing  areas  in  California  until  recently 
have  been  in  the  Imperial  Valley  and  in  the  vicinity  of  Los  Angeles. 
Within  the  past  two  or  three  years,  however,  many  new  lettuce  dis- 
tricts have  sprung  up  along  the  coast  and  in  the  interior  valleys. 
Lettuce  growing  in  many  of  these  new  districts  is  still  in  the  experi- 
mental stage.  It  will  take  some  time  to  determine  definitely  what 
regions  are  best  adapted  to  the  production  of  head  lettuce  of  high 
quality.  This  circular  is  intended  to  give  growers  in  the  newer  dis- 
tricts, many  of  whom  are  producing  lettuce  for  the  first  time,  informa- 
tion regarding  some  of  the  best  practices  in  the  older-producing  areas. 
The  main  need  of  the  industry  at  present  is  the  production  of  lettuce 
of  high  quality,  which  can  be  accomplished  only  by  a  wise  selection  of 
location  and  the  adoption  of  the  best  cultural  practices.  Poor  lettuce 
is  never  profitable  and  too  much  of  that  is  already  being  produced. 

Shipping  Seasons  for  California  Lettuce. — The  principal  shipping 
season  for  California  lettuce  is  during  the  late  fall,  winter,  and  early 
spring.  Most  of  the  lettuce  shipped  from  the  Imperial  Valley  moves 
during  late  December,  January,  February,  March  and  early  April.  The 
Los  Angeles  district  ships  the  greater  portion  of  its  crop  during 
November,  December,  April,  and  May,  before  and  after  the  movement 
of  lettuce  from  the  Imperial  Valley.  The  shipping  period  for  the  San 
Joaquin  Valley  practically  coincides  with  that  of  the  San  Fernando 
Valley.  The  development  of  new  districts  along  the  coast  in  Ventura, 
Santa  Barbara,  Santa  Cruz,  Monterey,  and  other  counties  has  made 
possible  the  shipment  of  lettuce  throughout  the  summer.  Many  of 
these  districts  are  temporary  because  they  are  not  adapted  to  growing 
this  crop  during  the  summer.  Nevertheless,  more  and  more  lettuce 
is  being  shipped  during  the  summer  months  as  new  districts  are  found 
that  are  suited  to  its  production.  Table  2  shows  the  carlot  shipments 
of  lettuce  for  California  by  months  for  the  years  1918  to  1924. 

TABLE  2 
Carlot  Shipments  of  Lettuce  for  California  by  Months  1918-1924 


Years 


Jan. 

Feb. 

Mar. 

Apr. 

May 

June 

July 

Aug. 

Sept. 

Oct. 

Nov. 

Dec. 

263 

471 

685 

162 

194 

43 

2 

8 

14 

12 

50 

147 

132 

295 

551 

555 

491 

69 

25 

11 

17 

96 

249 

240 

757 

1025 

985 

653 

870 

226 

74 

69 

52 

210 

851 

578 

1458 

1402 

1357 

1310 

897 

272 

202 

153 

139 

395 

987 

1174 

1312 

902 

1456 

2014 

1294 

391 

184 

104 

91 

220 

676 

1100 

2953 

2043 

3227 

1659 

1410 

430 

395 

507 

296 

450 

1241 

1502 

2256 

3185 

2461 

2291 

1952 

839 

380 

203 

279 

1080 

2015 

1461 

Total 

2051 
2731 
6350 
9746 
9744 
15113 
18404 


1918. 
1919. 
1920. 
1921. 
1922. 
1923. 
1924* 


Bureau  of  Agricultural  Economics. 


*  Subject  to  revision. 


CIRC.  295]         GROWING  AND  HANDLING  LETTUCE  IN  CALIFORNIA  5 

Distribution  of  California  Lettuce. — California  lettuce  is  widely 
distributed  throughout  the  United  States  and  Canada  at  most  seasons 
of  the  year.  California  summer  lettuce,  however,  is  not  always  so 
widely  distributed  as  the  winter  crop.  The  tendency  is  to  place  sum- 
mer lettuce  on  markets  nearby,  especially  if  the  carrying  quality  of 
the  product  is  uncertain.  Most  of  the  lettuce  is  shipped  in  carlots, 
but  there  is  a  considerable  quantity  moved  in  mixed  cars  to  centers 
of  small  consumption. 

CLIMATIC  AND  SOIL  REQUIREMENTS 

Temperature  Requirements. — Lettuce  of  high  quality  can  be  pro- 
duced only  where  the  temperature  of  the  soil  and  air  is  moderately 
cool  and  uniform.  This  requirement,  i.e.,  a  cool,  uniform  temperature, 
must  be  kept  in  mind,  especially  by  those  who  are  attempting  to  grow 
lettuce  during  the  summer  months.  Fluctuating  high  and  low  temper- 
atures are  not  conducive  to  good  growth.  High  temperatures  favor  the 
production  of  seed  rather  than  foliage,  cause  a  bitter  taste  in  the 
product,  produce  loose  heads,  and  accelerate  the  development  of 
lettuce  diseases.  During  the  early  stages  of  development,  lettuce  will 
tolerate  a  considerable  amount  of  frost,  but  if  severely  frosted  when 
mature  or  nearly  mature,  it  is  more  subject  to  disease  and  does  not 
stand  shipment.  Generally,  frosted  lettuce  needs  close  trimming,  and 
is  therefore  not  attractive.  The  maturing  plants  make  very  little 
growth  during  continued  frosty  weather,  and  although  they  become 
solid,  they  remain  small,  their  leaf  tips  are  injured,  and  they  bring 
a  comparatively  low  price. 

Moisture  Requirements. — Lettuce  must  have  an  adequate  supply 
of  moisture  throughout  the  growing  season.  However,  an  excessive 
amount  of  water  in  the  soil  is  not  desirable. 

Soil  Requirements. — Lettuce  is  grown  successfully  on  a  wide  range 
of  soil  types  from  clay  loams  to  sandy  loams  and  muck,  but  it  attains 
its  highest  quality  on  fertile  loam  soils  which  contain  much  organic 
matter.  Where  the  fall  crop  is  subject  to  high  temperatures  during 
the  early  part  of  the  growing  season,  or  where  it  matures  during  hot 
weather,  the  heavier  types  of  soil  should  be  used,  as  they  retain  mois- 
ture better  and  are  somewhat  cooler.  The  lighter  soils  should  be 
used  to  produce  the  crop  that  grows  and  matures  during  the  cool 
season  of  the  year.  Heavy  clay  soils,  though  difficult  to  work,  will 
yield  excellent  crops.  All  lettuce  land  should  be  well  drained  and 
properly  leveled  for  irrigation.  Land  which  has  been  in  alfalfa  for 
several  years,  usually  produces  large  crops  of  high  quality. 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


SOIL  IMPROVEMENT 

If  the  land  is  not  sufficiently  fertile  to  produce  a  fairly  rapid 
growth  and  a  large  firm  head,  it  should  be  improved  by  applying 
manure  or  commercial  fertilizers  or  both,  and  by  growing  cover  crops. 
The  plant  food  elements  should  be  present  in  available  form  and 
in  sufficient  amount  to  give  a  continuous  growth.  While  phosphorus, 
potash,  and  other  plant  food  elements  are  necessary,  the  one  usually 
needed  most  is  nitrogen. 

r 

/ 


*$&. 


Fig.  3. — Lettuce  growing  between  English  walnuts.     Los  Angeles  County. 


rJSfck—^ 


C?vop  Rotation. — "While  as  many  as  five  or  six  crops  of  good  lettuce 
have  been  grown  consecutively,  it  is  seldom  that  more  than  two  are 
profitable  without  some  sort  of  rotation.  Various  lettuce  diseases 
accumulate  in  the  soil  and  infect  succeeding  crops.  In  the  Imperial 
Valley,  alfalfa  has  been  used  commonly  in  the  rotation.  Lettuce  is 
often  planted  directly  on  alfalfa  sod,  but  more  often  after  an  in- 
tervening crop  of  cantaloupes.  The  second  year,  cantaloupes  or  some 
field  crop  like  cotton  or  grain  is  followed  by  another  lettuce  crop.  The 
third  year  after  growing  cantaloupes  or  some  field  crop,  the  land  is 
again  resown  to  alfalfa.  A  deep-rooted  legume  crop  if  followed 
by  a  series  of  shallow  rooted  non-legume  crops  makes  a  good  rota- 
tion.    Cantaloupes    and    grain    crops    draw   heavily    on    the    potash 


CIRC.  295]         GROWING  AND  HANDLING  LETTUCE  IN  CALIFORNIA  7 

and  phosphate  supply  of  the  soil,  while  lettuce  requires  a  good 
supply  of  nitrate  for  its  best  development. 

In  the  San  Fernando  Valley,  lettuce  is  grown  almost  entirely  as  an 
intercrop  among  decidious  fruit  and  English  walnut  trees,  as  shown  in 
Fig.  3.  It  is  planted  in  the  fall  when  the  foliage  is  off  the  trees,  so 
extreme  shading  does  not  occur.  Spring  lettuce  is  also  grown  after 
fall  crops  of  cauliflower,  tomatoes,  celery,  or  fall  lettuce.  Fall  lettuce 
often  follows  spring  potatoes.  In  Los  Angeles  county,  land  is  high- 
priced,  and  it  is  necessary  to  keep  it  occupied  with  crops  that  are 
highly  profitable. 

Manuring. — Probably  the  best  fertilizer  for  lettuce  is  barnyard 
manure.  It  is  usually  best  to  compost  the  manure  before  applying  to 
the  land,  especially  if  the  field  is  to  be  planted  with  lettuce  imme- 
diately. In  composted  manure,  more  of  the  plant  food  elements  are  in 
an  available  form ;  there  is  no  coarse  material  to  interfere  with  plant- 
ing and  cultivation ;  many  of  the  noxious  weed  seeds  have  been 
destroyed ;  and  there  is  no  heating  of  the  soil.  In  composting,  how- 
ever, an  effort  should  be  made  to  prevent  leaching  of  the  soluble  salts 
and  the  loss  of  ammonia  by  heating.  If  fresh  or  unrotted  manure  is 
used,  it  should  be  applied  and  plowed  or  disked  under  in  time  to 
allow  it  to  decompose  and  become  incorporated  with  the  soil.  Decom- 
position of  the  manure  after  it  has  been  plowed  under  may  be 
accelerated  by  flooding  the  land.  In  tests  carried  on  in  the  Imperial 
Valley,  an  application  of  10  tons  an  acre  of  barnyard  manure  increased 
the  total  yield  54  per  cent,  and  caused  the  lettuce  to  mature  two  to 
four  weeks  earlier,  and  produce  larger  heads  of  better  quality  than 
the  adjoining  unmanured  plots.  Excessive  applications,  however, 
especially  in  warm  weather,  will  often  cause  loose  heads.  Not  only 
does  barnyard  manure  supply  plant  food,  but  its  organic  matter 
lightens  the  heavier  soils,  which  improves  aeration  and  water  penetra- 
tion, and  increases  the  water  holding  capacity  of  light  soils,  which 
cuts  down  irrigation  costs  by  decreasing  the  number  of  irrigations 
needed. 

Green  Manure  Crops. — Where  manure  can  not  be  obtained  in 
sufficient  amount  to  supply  the  needed  organic  matter  and  plant  food, 
green  manure  crops  alone  or  green  manure  crops  in  conjunction  with 
commercial  fertilizers  may  be  used.  A  cover  crop  or  green  manure 
crop,  preferably  a  legume,  should  be  chosen  that  is  adapted  to  the 
local  climatic  conditions  and  that  produces  a  good  tonnage  of  vegetable 
matter.  It  is  better  to  grow  cover  crops  rather  than  to  let  the  fields  lie 
idle  during  a  part  of  the  year.    Such  crops  keep  down  the  weeds  and, 


8  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

besides  adding  to  the  total  organic  content,  help  conserve  the  soluble 
mineral  elements  of  the  soil,  especially  in  regions  of  heavy  winter 
rainfall.  They  prevent  erosion,  help  aerate  the  subsoil,  and  increase 
the  favorable  bacterial  flora  of  the  soil.  By  the  addition  of  organic 
matter,  they  improve  the  texture  and  increase  the  moisture-holding 
capacity  of  the  sandy  soils.  Brabham  cowpeas  and  Laredo  soybeans 
have  been  shown  to  be  the  best  summer  green  manure  crops  for  Im- 
perial Valley  conditions,  not  only  because  they  give  a  large  tonnage, 
but  because  they  are  resistant  to  nematode  attack.  It  is  important  to 
give  a  thorough  disking  before  plowing  under  the  green  manure  crops. 


Fig.  4. — Brabham  cowpeas  in  Imperial  Valley.  This  crop  will  yield  24  tons 
of  green  tops  to  the  acre,  outyielding  other  varieties  of  summer  legumes.  Brab- 
ham and  Iron  cowpeas  and  Laredo  soybeans  are  resistant  to  the  attacks  of 
nematodes. 

If  the  soil  is  dry,  irrigation  after  plowing  will  hasten  decomposition. 
This  must  be  fairly  complete  before  the  next  crop  is  planted,  otherwise 
injurious  results  are  likely  to  follow. 

Commercial  Fertilizer. — Many  of  the  growers  are  planting  green 
manure  crops  and  supplementing  them  with  commercial  fertilizers  to 
keep  the  soil  in  a  state  of  high  productivity.  The  three  constituents 
supplied  in  a  complete  fertilizer  are  nitrogen,  phosphorous,  and  potash. 
Any  one  or  all  of  these  may  be  supplied  in  the  organic  or  inorganic 
form.  In  the  inorganic  form,  the  elements  are  immediately  available 
to  the  plant,  while  in  the  organic  form,  the  complex  compounds  must 
undergo  decomposition  into  more  simple  forms  before  they  can  be 
absorbed  by  the  plant.  This  decomposition  or  change  is  effected  by 
different  bacterial  groups  in  the  soil.  When  the  temperature  of  the 
soil  is  low,  these  bacteria  function  slowly  or  not  at  all,  so  it  is  better, 
during  the  cooler  seasons  at  least,  to  apply  the  fertilizers  in  the 
inorganic  form. 


CIRC.  295]         GROWING  AND  HANDLING  LETTUCE  IN  CALIFORNIA 


9 


It  is  impossible  to  specify  a  single  kind  or  uniform  amount  of 
fertilizer  for  the  entire  state  or  for  any  large  district  within  the  state. 
It  is  best  for  each  grower  to  make  a  number  of  tests  on  his  own  farm 
to  determine  the  kind  of  fertilizers  to  use,  and  the  most  profitable 
amount  to  apply.  In  general,  it  is  the  lack  of  nitrogen  that  usually 
limits  the  growth  of  the  lettuce  plant.  Nitrogen  can  be  applied  in 
the  inorganic  form  as  nitrate  of  soda  or  sulphate  of  ammonia.  Tank- 
age, fish  meal,  cotton  seed  meal,  dried  blood,  and  other  compounds  can 
be  used  to  supply  the  organic  form.     A  complete  fertilizer  is  often 


Fig.  5. — Fertilizer  drill  used  to  apply  fertilizer  to  the  sides  of  the  lettuce 
beds.  A  plumber's  Y  of  two-inch  pipe  is  fastened  to  the  frame  underneath 
the  fertilizer  hopper  of  an  ordinary  combination  corn  planter  and  fertilizer  drill. 
This  facilitates  a  uniform  distribution  of  the  fertilizer  along  the  sides  of  the 
bed. 


broadcasted  or  drilled  in  after  plowing  and  before  the  beds  are  made, 
but  may  be  drilled  in  the  center  or  in  the  sides  of  the  bed  before  plant- 
ing the  seed.  Ammonium  sulphate  or  nitrate  of  soda  may  be  applied 
as  a  side  dressing  after  the  plants  have  been  thinned  and  until  about 
a  month  before  harvesting.  Usually  75  to  100  pounds  or  more  are  used 
to  the  acre  in  this  way  by  drilling  it  in  along  the  side  of  the  bed, 
as  shown  in  Fig.  5,  or  spreading  it  in  the  furrows  before  irrigation.  It 
is  usually  best  not  to  apply  large  amounts  of  nitrogen  after  the  heads 
have  started  to  form,  especially  in  warm  weather  as  the  heads  are 
liable  to  burst. 


10 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


PREPARATION  OF  LAND  PREVIOUS  TO  PLANTING 

Leveling. — It  is  essential  in  the  growing  of  lettuce  under  irrigation 
to  have  the  land  level  and  the  beds  of  a  uniform  height  so  that  water 
can  be  applied  without  flooding  certain  areas  and  leaving  others  high 
and  dry.  The  fall  should  be  gradual,  so  that  the  entire  bed  can  be 
well  moistened.  If  leveling  is  necessary  it  should  be  done  well  in 
advance  of  the  planting  season.  If  much  dirt  has  to  be  moved,  it  is 
best  to  make  a  test  irrigation  to  settle  the  soil  and  reveal  the  depres- 
sions and  elevations.    The  necessary  retouching  can  be  done  after  the 


^MLa 


Pig.  G. — After  applying,  a  shovel  cultivator  is  used  to  cover  the  fertilizer 
and  open  the  furrow  for  irrigation  water. 


soil  has  become  sufficiently  dry.  It  is  a  frequent  practice  after  leveling 
to  improve  the  places  where  the  top  soil  has  been  removed  by  means 
of  manure  or  a  commercial  fertilizer  and  a  cover  crop.  By  fol- 
lowing this  practice,  a  more  uniform  crop  of  lettuce  is  produced. 

Preparatory  Tillage. — In  general,  the  soil  should  be  plowed  and 
then  disked  and  harrowed  to  a  fine,  mellow  condition  before  the  seed 
beds  are  made.  It  is  difficult  to  make  good  beds  or  do  good  seeding  on 
a  cloddy  soil.  When  seeding  is  done  during  very  hot  weather,  how- 
ever, aeration  is  facilitated  and  better  stands  are  obtained  if  the  soil 
is  left  a  little  crumbly.  When  alfalfa  land  is  broken  up  preparatory 
to  putting  in  lettuce,  it  is  given  a  deep  plowing  several  months  in 
advance  and  allowed  to  remain  in  this  rough  condition  until  about  a 
month  before  planting.     A  second  plowing  is  then  given,  followed 


ClRC.  295]         GROWING  AND  HANDLING  LETTUCE  IN  CALIFORNIA 


11 


by  a  quick  irrigation.  As  soon  as  the  ground  is  dry,  it  is  disked  and 
then  leveled  with  a  float,  as  shown  in  figure  7,  after  which  the  beds 
are  made. 

The  soil  should  be  thoroughly  worked  before  planting.  A  common 
sequence  of  operations  for  land  that  has  just  grown  a  cultivated  crop 
is  plowing  about  eight  inches  deep,  a  double  disking,  and  floating, 
then  replowing,  disking,  cross  disking,  floating,  and  bedding. 


Fig.  7. — Floating  or  smoothing  the  ground  after  disking  just  before  making 
the   beds.      This   operation   lowers   the   high   places   and   fills   in   the   depressions. 

Making  the  Beds. — Practically  all  of  the  lettuce  in  the  irrigated 
regions  of  the  West  is  planted  on  raised  beds.  In  California,  the 
general  custom  is  to  grow  two  rows  on  a  bed  with  furrows  between 
the  beds  to  carry  the  irrigation  water.     In  some  Western  states  the 

k- ;u  inches m+ —-Z0  inches *\ 


rour 


JTQW 


"b: 


Irrigation 
Furrow 


3'Uf  i4_  inches  Y}:V*y3r. 

;':':.:^:  Ridqt  or    Bed'. 


Fig   8. — General   type    of   bed   and   furrow   used    in    the    growing    of    lettuce    in 
California.     Dimensions  vary  according  to  local  conditions. 


planting  of  single  rows  on  raised  beds  is  still  practiced.  Usually  a 
larger  yeld  is  produced  where  two  rows  are  grown  on  a  bed.  The  one 
row  bed,  however,  requires  somewhat  less  expense  for  cultivation. 
The  bed  and  furrow  system,  as  shown  in  figure  8,  facilitates  irrigation 
and  drainage  and  gives  good  aeration  about  the  plants. 


12 


UNIVERSITY   OF    CALIFORNIA — EXPERIMENT    STATION 


The  width  of  bed,  distance  between  beds,  and  depth  of  furrow 
vary  in  different  regions,  according  to  the  climatic  conditions  and  type 
of  soil.  The  beds  vary  from  18  to  20  inches  or  more  in  width,  and  the 
furrows  from  18  to  22  inches  or  more.  It  is  seldom  that  the  beds  are 
less  than  three  feet  from  center  to  center,  and  usually  they  are  further 
apart  than  this.  They  should  be  made  so  that  they  will  be  4  to  10 
inches  high  after  smoothing.      If  the  furrows  are  not  made  suffi- 


Fig.  9. — Throwing  up  lettuce  ridges  with  single  and  double  listers. 

ciently  deep,  there  is  danger  of  flooding  the  beds.  Inexperienced 
growers  have  a  tendency  to  make  them  too  shallow.  In  regions  where 
strong  dessicating  winds  are  prevalent,  and  on  light,  sandy  soils,  low 
beds  are  to  be  preferred,  as  they  expose  less  surface  and  retain  the 
moisture  better. 

A  number  of  different  implements  have  been  devised  to  make  the 
lettuce  beds  or  ridges.  A  disk,  turning  plow'  a  single  or  double  lister, 
as  shown  in  figure  9,  or  a  two  row  cultivator  equipped  with  large 
shovels  may  be  used.  Many  growers  throw  them  np  with  a  plow  or 
lister  and  level  them  with  a  drag  or  sled.     In  Imperial  Valley,  the 


ClRC.  295]         GROWING  AND  HANDLING  LETTUCE  IN  CALIFORNIA 


13 


Fig.  10. — Furrows  have  been  made  and  the  beds  are  ready  for 
shaping  and  planting. 

general  practice  is  to  make  the  furrows  with  a  single  lister  pulled  by 
two  horses,  or  with  a  double  or  triple  lister  behind  a  tractor.  The  beds 
are  then  shaped  with  a  sled  just  before  the  seed  is  planted.    Fig.  11). 


Fig.  11. — One  method  of  making  and  leveling  the  beds.     Disks  attached  to  the 
runners  in  front  help  to  make  the  furrows. 


14 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


VARIETY   TO   PLANT 

Practically  the  only  lettuce  grown  at  the  present  time  in  California 
for  shipment  is  the  New  York,  and  it  is  the  variety  upon  which  the 
reputation  of  Californian  lettuce  has  been  built.  It  is  also  known  as 
Los  Angeles,  Los  Angeles  Market,  AVonderful,  New  York  Special,  and 
Mountain  Iceberg.  According  to  Morse,*  this  variety  is  known  in 
Europe  as  Chou  de  Naples  or  Neapolitan  Cabbage.  The  shippers  and 
buyers  refer  to  this  variety  as  Iceberg.  The  variety  which  the  seedsmen 


Fig.   12. — A  specimen  of  New  York  lettuce,  practically  the  only  variety 
shipped  from  California. 

know  as  Iceberg  has  the  edges  of  the  leaves  tinged  reddish  brown, 
while  the  New  York  is  entirely  free  from  brown,  and  forms  a  some- 
what firmer  head.  The  true  New  York  variety,  as  shown  in  figure  12, 
is  a  crisp,  large  heading,  dark  green  variety  with  the  mature  head  of 
a  slightly  flattened  globe  shape.  Some  strains  of  New  York  have 
slightly  elongated  heads.  These  are  not  so  easy  to  pack  in  the  crate 
as  those  that  are  slightly  flattened,  and  are  not  so  well  received  on 
the  market.  However,  some  of  the  best  strains  of  lettuce  under  cer- 
tain climatic  conditions  fail  to  mature  heads  of  the  desired  shape. 


*  Morse,  Lester  L.     l '  Field  Notes  on  Lettuce. ' '     C.  C.  Morse  Seed  Co.,  San 
Francisco,  Cal.;  pp.  76,  1923. 


CIRC.  295]         GROWING  AND  HANDLING  LETTUCE  IN  CALIFORNIA 


15 


Practically  all  of  the  lettuce  seed  of  the  New  York  variety  is  pro- 
duced in  California,  Freshly  harvested  or  new  seed  does  not  ger- 
minate so  well  as  that  which  has  been  stored,  so  it  is  the  general  custom 
among  seedsmen  to  store  lettuce  seed  for  a  year  before  selling  it  to 
the  grower. 

SOWING  THE  SEED 

Various  tools  have  been  devised  for  sowing.  Usually  the  two  rows 
on  top  of  a  bed  are  sown  in  a  single  operation  by  implements  similar 
to  those  shown  in  figures  13,  14  and  15,  but  a  gang  of  four  planters 


Fig.  13. — This  tool  shapes  the  beds  and  plants  two  rows  of  seed  in  one  oper- 
ation. The  runners  are  sufficiently  long  to  hold  the  tool  steady  and  the  seeders 
are  flexible  enough  to  conform  to  the  slight  irregularities  of  the  bed.  Imperial 
Valley. 

can  be  used  if  the  two  beds  have  been  made  at  the  same  time,  as  shown 
in  figure  16.  If  the  planting  is  done  as  a  separate  operation  after 
the  beds  have  been  completed,  a  two  row  planter  that  straddles  the 
furrow  is  generally  used,  similar  to  the  one  shown  in  figure  17.  Hand 
pushed  drills  are  sometimes  used.  Most  growers  attach  two  planters 
to  the  sled  that  shapes  the  bed.    This  system  saves  time,  and  further- 


16 


UNIVERSITY    OP    CALIFORNIA EXPERIMENT    STATION 


more,  the  two  rows  of  lettuce  on  a  bed  are  exactly  the  same  distance 
apart  throughout  their  length.  This  facilitates  work  with  "stirrup" 
or  other  wheel  hoes  and  cultivators  on  top  of  the  beds.  It  also  makes 
easy  the  cultivation  of  the  furrows  and  sides  of  the  bed,  because  the 
plants  are  all  at  the  same  distance  from  the  edge. 


Fig.  14. — This  sled  is  used  to  shape  the  beds  and  to  plant  two  rows  on  the 
same  bed  in  one  operation.  The  lever  on  top  enables  the  driver  to  lift  the 
planters  when  turning  at  the  end  of  the  rows.  The  lettuce  rows  on  the  bed  are 
always  the  same  distance  apart,  making  possible  the  use  of  "stirrup"  weeders. 
Large  cultivators  can  be  used  that  work  the  top  and  sides  of  the  bed  in  one 
operation. 


Fig.  15. — This  tool  makes  the  furrows,  shapes  the  beds  and  plants  the  seed 

in  one  operation. 


CIRC.  295]         GROWING  AND  HANDLING  LETTUCE  IN  CALIFORNIA 


17 


Fig.  16. — A  machine  designed  to  complete  two  beds  and  plant  four  rows 
of  lettuce  in  one  operation. 


Fig.  17. — This  type  of  two-row  planter  is  sometimes  used  to  straddle  the  furrow. 


18  UNIVERSITY   OF    CALIFORNIA EXPERIMENT    STATION 

Lettuce  seed  is  very  small  and  should  be  sown  as  shallow  as  pos- 
sible, but  it  must  be  covered  with  sufficient  soil  to  insure  germination. 
It  will  not  germinate  at  high  temperatures  unless  the  soil  is  well 
aerated.  This  aeration  is  accomplished  by  leaving  the  seed  bed  slightly 
coarser  than  is  the  practice  during  the  cool  season  of  the  year. 

Very  thick  seeding  is  objectionable.  The  labor  cost  of  thinning  the 
thick  stand  of  plants  is  expensive;  and  there  is  the  additional  waste 
of  high  priced  seed.  From  one  to  one  and  one-half  pounds  of  seed  to 
the  acre  is  sufficient  if  all  the  seed  is  viable  and  the  soil  temperature 
and  moisture  conditions  are  favorable. 

The  distance  between  rows  should  not  be  less  than  ten  inches. 
Some  growers  space  the  rows  from  15  to  17  inches  to  give  room  for 
the  development  of  large  heads.  Where  the  rows  are  too  close  together 
on  top  of  the  bed,  cultivation  is  more  difficult  and  expensive,  various 
diseases  are  likely  to  develop,  and  the  mature  heads  are  usually  smaller. 
In  general,  the  plants  grow  better  when  they  are  not  too  near  the 
edge  of  the  bed. 

The  entire  field  should  not  be  seeded  at  one  time.  Preferably,  suc- 
cessive sowings  should  be  made  at  intervals  of  10  to  14  days  through- 
out the  lettuce  planting  season.  This  extends  the  marketing  of  the 
crop  over  a  longer  period  and  gives  a  more  uniform  distribution  of 
labor  in  both  packing  house  and  field  throughout  the  season. 


THINNING    AND    HOEING 

Lettuce  should  be  thinned  before  the  plants  start  to  crowd.  In  warm 
weather  this  may  be  three  weeks  after  planting,  but  in  cool  weather 
it  may  be  delayed  as  long  as  eight  weeks.  The  plants  are  blocked  out 
12  to  15  inches  apart  in  the  row  by  special  short  handled  hoes  and  at 
the  same  time  thinned  by  hand  to  one  in  a  place.  Plants  not  true 
to  type  should  be  removed  at  this  time.  It  is  best  to  give  the  plants 
plenty  of  room  in  the  row. 

Thinning  is  a  very  important  operation,  and  in  many  cases  when 
it  is  done  under  contract,  a  part  of  the  money  is  withheld  until  the 
job  is  finished  in  a  satisfactory  manner.  Beds  and  furrows  are  usually 
cultivated  before  thinning.  It  is  usually  stipulated  that  all  weeds 
left  by  the  cultivator  be  removed  by  those  doing  the  thinning,  that  the 
plants  stand  at  a  specified  distance  in  the  row,  and  that  no  doubles  be 
allowed  to  remain.  When  there  is  danger  of  damage  by  insects,  thin- 
ning should  be  delayed  until  the  pests  have  been  destroyed. 


CIRC.  295]         GROWING  AND  HANDLING  LETTUCE  IN  CALIFORNIA 


19 


After  thinning  it  is  necessary  to  hoe  to  kill  the  weeds,  remove 
doubles,  and  re-thin  where  it  is  needed.  In  hoeing,  the  soil  should  not 
be  pulled  up  to  the  plants,  as  this  obstructs  free  circulation  of  air  and 
facilitates  the  development  of  diseases. 


IRRIGATION  AT  PLANTING  TIME 


The  system  of  irrigation  used  at  time  of  planting  varies  with  the 
locality  and  with  the  climatic  and  soil  conditions,  (1)  In  some  regions 
the  land  is  flood  irrigated,  the  beds  are  made,  and  the  seed  is  planted 
and  no  further  irrigation  is  given  until  the  seedlings  are  through  the 


Fig.  18. — Irrigating  lettuce  beds.  Water  enters  the  furrows  from  the  head 
ditch  through  small  conduits.  Usually  only  one  is  used  for  each  furrow.  The 
pieces  of  shook  beside  the  opening  is  used  to  regulate  the  flow.     Imperial  Valley. 

soil.  This  system  can  be  practiced  where  the  soil  dries  out  slowly. 
(2)  Where  evaporation  is  very  high,  in  addition  to  the  preliminary 
flood  irrigation,  it  is  the  practice  to  irrigate  immediately  after  plant- 
ing. Beds  made  of  moist  soil  settle  more  evenly  after  irrigation  than 
when  made  of  loose,  dry  soil.  (3)  Rough  beds  are  sometimes  made  in 
land  that  has  not  received  a  preliminary  flooding.  The  beds  are  wet 
by  running  water  in  the  furrows,  as  shown  in  figure  18.  This  irriga- 
tion moistens  and  settles  the  beds  which  when  sufficiently  dry  are 
smoothed  and  planted.  (4)  Seed  is  sometimes  planted  in  dry  soil  that 
is  irrigated  only  after  the  seed  is  planted.  This  is  probably  the  least 
satisfactory  method  of  all,  as  the  beds  usually  settle  unevenly  at  the 
first  irrigation  and  during  subsequent  irrigations  there  is  danger  of 
flooding. 


20 


UNIVERSITY   OF    CALIFORNIA — EXPERIMENT    STATION 


When  furrow  irrigating,  the  water  should  be  allowed  to  sub  through 
the  beds  and,  if  given  time,  it  will  finally  moisten  the  entire  bed.  Irri- 
gating the  beds  immediately  after  planting,  as  shown  in  figure  19, 
is  usually  preferred  in  warm  dry  weather.  The  water  is  often  kept 
running  in  small  streams  down  the  furrows  until  the  plants  are  up. 
This  cools  the  soil  and  produces  a  higher  percentage  of  germination. 
In  cool  weather  such  heavy  irrigation  immediately  after  planting  is 
not  necessary.  In  heavy  clay  soils,  deep  furrows  are  used  with  a 
small  head  of  water.  If  the  water  comes  up  close  to  the  top  of  the 
bed,  the  soil  will  bake  and  crack  when  it  dries  and  the  seedlings  will 
not  come  through. 


Fig.  19. — The  seed  has  been  planted  and  the  beds  are  being  irrigated.  Irriga- 
tion immediately  after  planting  is  an  important  operation  in  most  of  the  lettuce 
producing  areas  of  California. 

Regardless  of  location,  however,  the  soil  about  the  seed  and  above 
it  should  be  kept  moist  until  the  seeds  have  germinated  and  the  seed- 
lings are  through  the  soil.  More  care  must  be  exercised  in  getting 
the  plants  up  in  the  hot  arid  regions  than  along  the  coast,  where  the 
sea  breezes  and  cool  temperatures  prevent  rapid  evaporation.  The 
time  and  method  of  irrigation  depend  largely  upon  the  climatic  and 
soil  conditions. 


IEEIGATING  THE  GEOWING  CEOP 


The  details  of  irrigation  practice  very  considerably  in  different 
localities  and  at  different  times  of  the  year.  It  is  best  to  irrigate  very 
sparingly  when  the  plants  are  small,  as  this  will  make  the  lettuce 


ClEC.  295]         GROWING  AND  HANDLING  LETTUCE  IN  CALIFORNIA  21 

develop  a  deep  instead  of  a  shallow  root  system.  If  too  much  water 
is  applied  when  the  heads  are  maturing,  they  are  liable  to  be  soft  and 
loose.  Heavy  rains  just  before  cutting  time  often  cause  the  develop- 
ment of  open  spongy  heads.  Small  plants  need  much  less  water  than 
larger  ones.  Less  water  is  required  when  the  weather  is  cool,  and 
humid,  than  when  hot,  dry,  and  windy.  The  frequency  of  irrigation 
of  lettuce  also  depends  on  the  water-holding  capacity  of  the  soil  and 
the  slope  of  the  land.  More  frequent  irrigations  are  needed  on  light 
sandy  soils  than  on  the  sandy  or  clay-loam  soils  which  are  more 
retentive  of  moisture. 


Fig.  20. — Irrigation  and  drainage  ditches.  The  drainage  ditch  at  the  right 
is  carrying  off  the  water  after  it  has  passed  down  between  the  beds.  The 
irrigation  ditch  at  the  left  is  ready  to  receive  water  and  conduct  it  to  the  fur- 
rows between  the  beds.  A  more  uniform  control  of  moisture  conditions  can  be 
obtained  if  the  rows  are  not  too  long.  Cross  ditches  for  irrigation  and  drainage 
facilitates  the  equable  distribution  of  water. 

While  it  takes  some  experience  to  tell  just  when  lettuce  needs  water, 
in  general,  the  plants  are  suffering  for  lack  of  water  when  they  take  on 
a  dark  green  color  and  the  leaves  look  and  feel  tough  and  leathery. 
AVhen  the  moisture  supply  is  plentiful,  the  leaves  are  crisp  and  have 
a  light  green  color.  During  frosty  weather,  growers  commonly  prac- 
tice night  irrigation  to  raise  the  temperature  of  the  air  around  the  let- 
tuce. 

Devices  for  Regulating  Water  Flow. — Most  of  the  growers  use  a 
series  of  small  wooden  conduits  or  flumes  to  carry  a  small  stream  of 
water  from  the  end  ditch  to  the  furrows  between  the  beds.  A  conduit 
is  made  of  four  laths  or  slightly  wider  strips  20  to  24  inches  long, 
nailed  together.    It  should  be  sufficiently  long  to  fit  well  in  the  ditch 


22 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


bank.  Pieces  of  shook  or  lath  can  be  placed  in  front  of  the  conduits 
to  regulate  the  flow.  Galvanized  or  iron  pipes  cut  to  the  same  length 
as  the  wooden  conduits  are  often  used.  Iron  pipes  are  more  permanent 
and  sizes  from  l1/^  to  IV2  inches  in  diameter  are  generally  used. 

CULTIVATION 

Irrigation  should  never  take  the  place  of  cultivation.  A  mistake 
often  made  by  inexperienced  growers  is  to  apply  water  when  a  good 
cultivation  is  needed  instead.     Too  frequent  irrigations  keep  the  soil 


Fig.  21. — Cultivating  lettuce.  The  cultivator  on  the  right  works  the  top  and 
sides  of  the  bed  and  precedes  the  cultivator  on  the  left,  Avhieh  stirs  the  soil  in 
the  furrows. 


wet  and  cold,  while  cultivation  helps  to  warm  it  by  facilitating  aera- 
tion. The  soil  should  be  cultivated  after  each  irrigation  and  before  a 
hard  crust  has  formed.  As  the  lettuce  plant  is  a  shallow  feeder  and  a 
rather  poor  forager,  care  must  be  taken  not  to  injure  the  root  system 
by  deep  cultivation,  especially  during  the  later  stages  of  growth. 
A  majority  of  the  growers  stop  cultivating  at  least  a  week  or  ten  days 
before  harvesting  commences,  in  order  not  to  disturb  the  extensive 
system  of  feeder  roots  growing  close  to  the  surface  of  the  ground. 
The  most  common  practice  is  to  cultivate  the  furrows  and  sides  of  the 
bed  with  a  one-horse  cultivator  as  soon  after  irrigating  as  possible. 
This  operation  partially  fills  the  furrows,  which  makes  it  necessary  to 
open  them  up  before  the  next  irrigation. 


CIRC.  295]         GROWING  AND  HANDLING  LETTUCE  IN  CALIFORNIA 


23 


In  some  districts  an  implement  like  the  one  shown  in  figure  21 
is  used  to  cultivate  the  soil  between  the  rows  of  lettuce  on  the  bed  and 
in  the  furrows  at  the  same  time.  Regular  beet  cultivators  and  small 
wheel  hoes  are  frequently  used  to  cultivate  the  beds.  Care  must  be 
taken  not  to  cover  the  plants  or  to  pull  dirt  away  from  the  edge  of  the 
beds  and  expose  the  root  systems.     (See  fig.  22). 


Fig.  22. — A  lettuce  cultivator  in  use  in  the  Pajaro  Valley.  A  plank  is  rounded 
to  fit  in  the  furrows.  There  are  nine  harrow  teeth  and  an  adjustable  knife  in 
the  rear.     This  type  of  cultivator  does  not  throw  dirt  on  the  lettuce  plant. 


YIELD 

The  yield  varies  considerably  from  year  to  year.  Over  a  five- 
year  period,  from  1919  to  1923,  the  average  number  of  crates  to 
the  acre  for  California  was  249,  258,  335,  208  and  222,  respectively. 
This  gives  some  indication  of  the  number  of  crates  that  may  be 
expected. 


HAEVESTING 

( 1 )  Harvesting  should  not  be  done  until  the  heads  are  ' '  mature ' ' — 
(firm).  Immature  heads  wilt  more  readily.  In  cutting  lettuce  imma- 
ture, the  grower  ruins  the  market  for  the  high  grade  product.  When 
ready  to  be  cut,  the  tops  of  the  mature  heads  are  lighter  colored  than 
those  of  the  immature,  and  have  a  silvery  appearance. 


24 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


(2)  Lettuce  should  be  cut  just  below  the  surface  of  the  ground, 
as  shown  in  figure  23.  The  most  of  the  triming  of  the  outer  leaves 
should  be  done  at  the  packing  shed. 

(3)  Lettuce  is  usually  cut  by  contract  labor.  A  gang  of  cutters 
go  down  the  rows  cutting  the  matured  heads  and  tossing  them  into 
every  third  furrow  with  stems  up  so  as  to  allow  the  moisture  in  the 
head  to  drain  out.  A  second  gang  of  men  then  pack  the  heads  tightly, 
with  stems  up,  into  crates  as  indicated  in  figure  24,  and  load  them  on 
wagons.    The  crates  are  then  hauled  to  the  packing  shed. 


•-■  ^JS        l        V,       "JON 


Fig.   23. — Harvesting  lettuce,   showing  the  type   of  knife  used  and  the 
method  of  cutting  off  the  root  just  below  the  ground. 

(4)  Lettuce  should  not  be  cut  for  shipment  immediately  after  a 
rain  or  an  irrigation,  or  until  the  frost  and  dew  is  gone  in  the  morning. 
When  the  plants  are  gorged  with  water,  the  leaves  are  crisp  and  brittle 
and  break  easily  in  handling.  Lettuce  heads  that  are  just  slightly 
wilted  are  injured  less  in  handling  and  packing,  and  carry  better  in 
transit.    Lettuce  should  not  be  cut  when  the  field  is  muddy. 

(5)  Lettuce  heads  that  show  signs  of  development  of  seed  stalk, 
that  have  burst,  have  tip  burn,  or  show  signs  of  disease  infection  should 
be  discarded  in  the  field. 

(6)  Growers  should  not  attempt  to  harvest  all  the  heads  in  the 
field  at  one  cutting.  Several  cuttings  must  be  made  to  obtain  all  heads 
at  the  best  stage  of  maturity. 

(7)  Lettuce  should  not  be  delivered  to  the  packing  shed  in  a  badly 
wilted  condition.     When  the  haul  to  the  packing  shed  is  long,  the 


CIRC.  295]         GROWING  AND  HANDLING  LETTUCE  IN  CALIFORNIA 


25 


crates  should  be  covered  with  heavy  muslin  or  canvas.  The  crates  in 
the  field  should  not  be  filled  too  full,  otherwise  there  is  danger  of 
crushing  or  bruising  by  pressure  from  crates  stacked  on  top.  Figure 
25  shows  the  usual  method  of  hauling  the  crates  of  lettuce  from  the 
field,  they  are  then  transferred  to  large  auto  trucks,  similar  to  those 
shown  in  figure  26,  and  hauled  to  the  packing  shed. 


Fig.  24. — Placing  lettuce  in  crates  for  delivery  to  the  packing  shed.  Heads 
are  cut  and  thrown  into  alternate  furrows.  They  are  then  gathered  into  small 
piles  and  packed  tight  into  crates  for  the  trip  to  the  packing  shed.  The  crates 
should  not  be  packed  too  full. 


Fig.  25. — Hauling  lettuce  from  the  field. 


26 


UNIVERSITY   OF    CALIFORNIA EXPERIMENT    STATION 


(8)  There  is  at  times  a  tendency  to  harvest  the  lettuce  before  it 
has  matured,  especially  if  the  price  is  high.  Small  heads  of  poor 
quality  invariably  bring  a  low  price  on  the  market.  Most  growers 
now  realize  that  money  is  lost  by  premature  harvesting.  Mature 
lettuce  can  remain  in  the  field  for  a  long  time  without  bursting  when 
the  weather  is  cool.  In  very  warm  weather  or  when  freezes  are 
expected,  lettuce  should  be  harvested  as  soon  as  it  is  mature. 


■'^. 


■ftlv^:. 


Fig.  26. — If  long  hauls  are  made  the  crates  are  transferred  to  large  auto 
trucks  at  the  edge  of  the  field.  If  exposed  to  the  sun  for  a  considerable  period 
especially  during  warm  weather  the  load  is  usually  covered  with  a  canvas. 


PACKING  FOR  SHIPMENT 

At  the  packing  shed,  the  loose,  diseased,  and  damaged  leaves  are 
trimmed  off,  as  shown  in  figure  27,  and  the  small  or  loose  heads  culled 
out.  Too  many  wrapper  leaves  should  not  be  removed  as  this  increases 
the  danger  of  bruising.  When  trimmed,  the  heads  are  tossed  on  to  the 
packing  table,  where  they  are  placed  in  crates,  as  shown  in  figure  28. 
They  are  usually  packed  in  the  "Los  Angeles"  crate,  which  is  24V2-in. 
by  18-in.  by  13-in.,  or  in  the  "Imperial  Valley"  crate,  which  has  the 
same  outside  dimensions,  but  is  longer  inside.  From  2%  to  7  dozen 
are  put  in  each  crate,  according  to  the  size  of  the  heads. 

The  lettuce  crate  is  lined  with  two  strips  of  heavy  water-proofed 
paper,  which  cover  the  bottom,  sides,  and  ends  and  fold  over  the  top 
to  protect  the  contents  from  dirt  and  infection,  to  keep  the  lettuce 


ClRC.  295]         GROWING  AND  HANDLING  LETTUCE  IN  CALIFORNIA 


27 


cool  and  fresh,  and  to  prevent  mechanical  injuries  to  the  heads.  Three 
layers  of  heads  are  packed  tight  in  the  crate  with  stems  up,  generally 
with  cracked  ice  between  the  layers,  as  shown  in  figure  29.  Usually 
not  over  30  pounds  of  ice  is  used  in  each  crate.  The  crates  should  be 
placed  in  the  refrigerator  car  as  soon  as  packed.     From  4500  to  7500 


Fig.  27. — Trimming  lettuce.     The  butts  and  damaged  or  diseased  leaves  are 
trimmed  off.     The  waste  leaves  are  used  for  poultry,  cattle  or  hog  feed. 

pounds  of  ice,  according  to  the  weather,  is  placed  in  the  car,  usually 
on  top  of  the  crates  in  the  car  instead  of  in  the  bunkers.  A  slight 
bulge,  as  shown  in  figure  30,  is  given  the  crate  so  that  the  heads  will 
not  move  about  in  the  container.  The  usual  carload  is  320  standard 
crates,  which  are  stacked  5  wide,  4  high,  and  16  long,  each  stack  being 
securely  "stripped"  together  and  braced  well  between  the  two  halves 
of  the  car  to  prevent  sliding  and  moving. 


28 


UNIVERSITY   OF    CALIFORNIA EXPERIMENT    STATION 


GRADING  AND  STANDAEDIZATION 

The  permanent  success  of  the  California  lettuce  industry  can  be 
assured  only  by  placing  upon  the  market  a  product  of  high  quality, 
that  is  rigidly  graded  and  highly  standardized. 


Fig.  28. — Packing  and  trimming  in  the  packing  shed.  In  the  background 
the  men  are  cutting  back  the  stems,  and  removing  the  diseased  and  damaged 
leaves.  The  trimmed  heads  are  then  tossed  on  to  a  low  table  in  reach  of  the 
packers. 


Fig.  29. — Cracked  ice  is  placed  between  the  layers  of  lettuce  when  packed. 
From  25  to  30  pounds  of  ice  are  used  in  each  crate.  This  cools  the  lettuce  and 
tends  to  insure  its  reaching  the  eastern  markets  in  good  condition. 

Californian  shippers  are  not  required  to  use  any  specified  grades 
but  the  value  of  rigid  grading  is  so  apparent  that  most  of  the  shippers 
have  voluntarily  adopted  the  Federal  Grades. 


CIRC.  295]         GROWING  AND  HANDLING  LETTUCE  IN  CALIFORNIA 


29 


U.   S.    GRADES   FOR   LETTUCE 


U.  S.  Fancy 

U.  S.  No.  1 

U.  S.  No.  2 

Shall  consist  of 

Shall  consist  of 

Shall  consist  of 

Heads  of  Lettuce 

Heads  of  Lettuce 

Heads  of  Lettuce 

WHICH  ARE 

WHICH  ARE 

WHICH  ARE 

of  similar  varietal 

of  similar  varietal 

of  similar  varietal 

characteristics 

characteristics 

characteristics 

fresh 

fresh 

fresh 

well  trimmed 

well  trimmed 

OF  REASONABLE 
SOLIDITY 

SOLID 

WHICH  ARE  NOT 

WHICH  ARE  NOT 

WHICH  ARE  NOT 

decayed 

decayed 

decayed 

split 

split 

burst 

burst 

burst 

WHICH  ARE  FREE 

WHICH  ARE  FREE 

WHICH  ARE  FREE 

FROM 

FROM 

FROM 

seed  stems 

seed  stems 

seed  stems 

DOUBLES 

DOUBLES 
FREEZING  DAMAGE 

FREEZING  DAMAGE 

SERIOUS  FREEZING 

DAMAGE 

damage  caused  by  dirt 

damage  caused  by  dirt 

damage  caused  by  wilting 

damage  caused  by  wilting 

wilting  damage  caused  by 

tip  burn  damage 

tip  burn  damage 

tip  burn  damage 

disease  damage 

disease  damage 

disease  damage 

insect  damage 

insect  damage 

insect  damage 

mechanical  damage 

mechanical  damage 

mechanical  damage 

damage  by  other  means 

damage  by  other  means 

damage  by  other  means 

In  order  to  allow  for  variations  incident  to  proper  grading  and  handling,  not 
more  than  10  per  cent,  by  count,  of  any  lot  may  be  below  the  requirements  of 
these  grades. 

DEFINITION  OF  TERMS 

As  used  in  these  grades : 

"Similar  varietal  characteristics"  means  that  the  heads  in  any 
container  have  the  same  color  and  characteristic  leaf  growth.  For 
example,  lettuce  of  the  Iceberg  and  Big  Boston  types  must  not  be 
mixed. 

"Fresh"  means  crisp  and  green. 

"Well  trimmed"  means  that  the  coarse  and  damaged  outer  leaves 
have  been  removed,  leaving  the  head  protected  by  green  wrapper 
leaves.  Heads  which  show  a  considerable  number  of  wrapper  leaves 
in  excess  of  those  required  to  protect  the  head  shall  not  be  regarded 
as  well  trimmed.  Heads  showing  a  ragged  appearance  caused  by  the 
removal  of  portions  of  the  outside  leaves  shall  not  be  considered 
U.  S.  No.  1. 


30 


UNIVERSITY   OF    CALIFORNIA — EXPERIMENT    STATION 


"Seed  stems"  means  those  heads  which  have  seed  stems  showing 
or  in  which  the  formation  of  seed  stems  has  plainly  begun. 

"Solid"  shall  be  interpreted  as  "hard"  for  Iceberg  type  and 
"firm"  for  the  Big  Boston  type. 

"Of  reasonable  solidity"  shall  be  interpreted  as  "firm"  for  Iceberg 
type  and  "fairly  firm"  for  Big  Boston  type. 

' '  Fairly  firm ' '  means  that  the  head  is  well  formed  and  not  soft  or 
spongy. 

' '  Free  from  damage ' '  means  that  the  heads  shall  not  be  injured  to 
an  extent  readily  apparent  upon  examination. 

"Free  from  serious  damage"  means  free  from  any  injury  which 
causes  a  loss  of  a  portion  of  the  edible  part  of  the  head.  The  loss  of 
the  crispness  due  to  freezing  shall  not  be  considered  serious  damage. 


Fig.  30. — Loading  car  with  lettuce.  Crates  are  stacked  4  deep,  5  wide,  and 
16  long,  and  are  held  firm  by  wooden  strips.  Ice  is  placed  on  top  of  the  upper 
tier  of  crates.     Figure  also  shows  a  packed  crate  with  the  desirable  bulge. 


INSPECTION* 

"In  July,  1920,  there  was  established  in  California  a  commercial 
shipping-point  inspection  service  carried  on  by  the  Bureau  of  Stand- 
ardization of  the  State  Department  of  Agriculture.  This  service  em- 
ploys a  corps  of  experienced,  highly  trained  men  who  are  authorized  to 
inspect  and  certify  to  the  exact  quality  and  condition  of  the  produce 
at  time  of  packing  and  shipping.  The  demand  for  this  service  has 
increased  steadily   and  its  scope  and  importance   has  been   greatly 


*  Successful    marketing    of    the    California    Vegetables.      Special    Publication 
No.  32,  California  State  Department  of  Agriculture. 


ClRC.  295]         GROWING  AND  HANDLING  LETTUCE  IN  CALIFORNIA  31 

enlarged.  *  *  *  On  July  1,  1922,  this  service  was  federalized,  each 
inspector  being  deputized  by  the  federal  government,  and  certificates 
issued  are  now  prima  facie  evidence  in  all  courts  of  the  United  States. ' ' 
"This  inspection  is  available  in  all  of  the  leading  vegetable  pro- 
ducing sestions  of  the  state.  The  certificate  shows  the  hour  and  date 
of  inspection,  inspection  or  shipping  point,  name  and  address  of  the 
shipper  and  consignee  (when  given),  car  initials  and  number,  kind  of 
car  and  its  condition;  if  a  refrigerator,  the  amount  of  ice  in  the 
bunkers;  the  quantity  of  the  products  inspected;  description  of  load 
and  container;  condition  of  pack;  sizing,  quality  and  condition  of 
the  products;  color,  grade  remarks.  The  buyer,  therefore,  knows  the 
exact  quality  and  condition  of  the  product  at  the  time  the  car  is 
loaded,  although  he  may  be  at  a  considerable  distance  from  the 
shipping  point.  These  shipping-point  certificates  are  valuable  to  the 
grower,  as  they  protect  his  interests  in  the  adjustment  of  claims  or  on 
a  declining  market.  On  the  other  hand,  the  buyer  is  assured  that  he 
will  receive  the  quality  of  produce  for  which  he  has  paid  before 
seeing  it.  Whenever  requested,  a  telegram  giving  the  substance  of  an 
inspection  will  be  sent  "collect"  to  the  buyer  or  any  other  interested 
party,  so  that  the  exact  condition  of  a  carload  can  be  ascertained 
before  the  sale  is  even  consummated." 

INSECT  PESTS  AND  THEIR  CONTROL 

Cutworms. — Probably  the  most  common  serious  pest  that  the  grow- 
ers of  lettuce  have  to  contend  with  is  the  cutworm.  The  most  damage 
is  done  while  the  plants  are  small,  the  young  plants  usually  being  cut 
off  at  the  ground  level.  The  best  protection  obtained  has  been  by 
using  poisoned  bait.    The  following  formula  is  recommended : 

Paris    Green    (or    white    arsenic) 1  pound 

Molasses    (cheap   black   strap) 2  quarts 

Water    4  gallons 

Wheat   bran   25  pounds 

The  addition  of  %  of  an  ounce  of  amyl  acetate  of  the  technical  No. 
1  grade  to  this  formula  has  been  found  advantageous  in  the  Imperial 
Valley.  In  preparing  the  mash,  the  amounts  should  be  measured 
carefully.  The  white  arsenic  or  Paris  Green  should  be  thoroughly 
stirred  with  the  molasses  and  water.  This  poisoned  mixture  should  be 
poured  over  the  bran  and  stirred  thoroughly.  Enough  water  should 
be  added  to  make  a  crumbly,  but  not  a  wet  mash.  When  squeezed  in 
the  hand,  only  two  or  three  drops  should  come  out.  This  mash  should 
be  spread  on  top  of  the  beds  near  the  plants  in  the  early  evening,  as 
cutworms  do  most  of  their  damage  at  night.    Dusting  or  spraying  the 


32  UNIVERSITY   OF    CALIFORNIA — EXPERIMENT    STATION 

plants  with  arsenate  of  lead  is  useful  when  the  plants  are  young,  but 
should  never  be  practiced  when  the  crop  is  approaching  maturity. 

A  severe  infestation  of  cutworms,  alfalfa  semi-loopers,  and  cater- 
pillars of  the  yellow  alfalfa  butterfly  occurred  in  the  Imperial  Valley 
in  1923.  The  growers  at  that  time  were  able  to  bring  their  fields 
through  in  good  condition  by  observing  certain  recommended  practices. 
If  the  lettuce  pests  mentioned  above  are  present  in  large  numbers,  the 
field  should  be  dusted  or  sprayed  with  lead  arsenate  before  thinning. 
If  the  attack  is  especially  severe,  arsenate  of  lead  should  be  dusted  on 
undiluted.  If  the  pests  are  not  especially  abundant,  satisfactory 
results  can  be  obtained  by  using  a  mixture  containing  one  part  of 
arsenate  of  lead  and  four  parts  of  powdered  air-slacked  lime,  finely 
ground  gypsum,  sulfur,  or  cheap  flour.  Dusting  is  probably  better 
than  spraying. 

Grasshoppers. — Grasshoppers  sometimes  devour  entire  fields  of 
young  fall  planted  lettuce.  It  should  be  the  regular  practice  of  all 
growers  to  burn  the  grass  and  weeds,  and  to  work  the  ground  along 
the  roads  and  ditch  banks  adjoining  their  fields,  as  the  female  grass- 
hoppers lay  their  eggs  in  the  surface  of  the  soil  of  these  untilled 
areas.  As  much  trouble  may  be  expected  from  grasshoppers  where 
lettuce  fields  adjoin  alfalfa  or  pasture  lands,  some  arrangement  should 
be  made,  if  possible,  to  have  these  fields  thoroughly  disked  or  harrowed. 
When  alfalfa  land  is  being  broken  up  for  lettuce,  it  should  be  disked 
or  harrowed  before  plowing  in  order  to  destroy  the  eggs  of  grass- 
hoppers and  other  insects  and  the  pupal  stages  of  cutworms. 

When  grasshoppers  appear  in  the  field,  a  heavy  irrigation  should 
be  given  to  moisten  the  ground  thoroughly.  The  best  way  to  fight 
grasshoppers  is  to  use  the  poison  bran  mash  recommended  for  cut- 
worms with  the  addition  of  V/2  dozen  chopped  lemons  and  1  pound  of 
salt.  The  substitution  of  i/o-pound  of  sodium  arsenite  for  the  Paris 
Green  is  also  recommended.  This  mash  should  be  spread  in  the  early 
morning,  as  grasshoppers  do  most  of  their  feeding  during  the  day. 

BIEDS 

Hundreds  of  acres  of  young  lettuce  are  sometimes  devoured  by 
English  sparrows  in  some  sections  of  the  state.  Probably  the  best 
method  of  controlling  these  pests  is  to  erect  a  large  number  of  small 
scarecrows  throughout  the  field  in  the  form  of  bright  pieces  of  cloth 
or  paper  fastened  to  laths  or  sticks,  and  in  addition  to  use  a  shotgun 
for  a  day  or  two.  Good  results  will  be  obtained  by  using  small 
kernelled,  or  cracked  wheat,  lettuce  seed,  or  "bird  seed"  coated  with 
strychnine.    Good  results  have  been  obtained  also  by  use  of  a  formula 


CIRC.  295]         GROWING  AND  HANDLING  LETTUCE  IN  CALIFORNIA  33 

recommended  by  the  United  States  Department  of  Agriculture.  To 
one-eighth  ounce  of  pulverized  strychnine  dissolved  in  three-fourths 
of  a  gill  of  hot  water,  one  and  a  half  teaspoonfuls  of  starch  or  wheat 
flour  moistened  with  a  few  drops  of  cold  water  are  added.  This  mix- 
ture is  heated  while  constantly  stirring  until  it  thickens.  It  is  then 
poured  over  one  quart  of  wheat  and  stirred  until  every  kernel  is  coated. 
This  should  be  distributed  over  the  areas  in  the  field  where  the  birds 
are  feeding. 

DISEASES 

Tip-barn. — Tip-burn  is  a  non-parasitic  disease  and  is  most  likely 
to  be  prevalent  during  the  summer,  especially  when  warm  bright  days 
follow  a  period  of  foggy  or  cloudy  weather.  In  a  preliminary  report, 
Rawlins  and  McClain*  state  that  ' '  the  first  evidence  of  the  trouble  is 
usually  the  development  of  small  brown  spots  near  the  edge  of  the 
upper,  more  tender  exposed  leaves.  These  spots  usually  develop  first 
at  the  junction  of  small  veins  about  one-quarter  to  one-half  inch  from 
the  edge  of  the  leaf.  The  development  of  these  small  dead  spots  seems 
to  prevent  the  passage  of  water  to  the  edges  of  the  leaf  and  that  por- 
tion outside  of  the  spots  becomes  wilted  and  yellow  and  soon  dies, 
leaving  a  dead,  brown  strip  around  the  edge  of  the  leaf.  The  only 
practical  way  in  which  the  farmer  may  hope  to  evade  tip-burn  during 
the  warmer  months  is  through  the  use  of  resistant  varieties.  The  most 
promising  variety  showing  resistant  qualities  is  Iceberg. ' ' 

Slimy  Soft  Rot  or  Slime. — Slime  is  a  disease  caused  chiefly  by  the 
fungus  Botrytis,  although  a  number  of  bacteria  have  been  found 
associated  with  it.  The  disease  appears  in  the  field,  in  transit,  and  in 
storage,  and  is  characterized  by  a  slimy  and  slippery  condition  of  the 
affected  parts  and  by  a  very  offensive  odor.  Tissues  of  lettuce  are  pre- 
disposed to  slime  by  the  bruising  of  the  leaves  during  handling,  by 
frost  injury,  by  tip-burn,  and  sun-scald.  In  the  field  the  control  of 
slime  usually  resolves  itself  into  the  control  of  tip-burn.  In  transit, 
it  can  be  kept  in  check  by  packing  only  healthy  and  uninjured  heads 
and  by  shipping  under  dry,  cool  conditions.  It  is  impossible  to  keep 
the  heads  dry,  however,  with  our  present  methods  of  handling. 

Downy  Mildew. — Downy  mildew  is  caused  by  the  fungus  Bremia 
lactucae.  The  first  indications  of  the  disease  appear  a  slight  green 
or  yellowish  areas  on  the  upper  surface  of  the  leaf.  On  the  under 
side  of  these  discolored  areas  there  soon  appears  a  downy  white  growth 
of  mold.    The  older  diseased  areas  take  on  a  brown  color.    Milbrathf 


*  Tip-burn  and  slime  disease  of  lettuce.    Pacific  Rural  Press,  March  14,  1925. 
t  Downy  mildew  on  lettuce  in  California.      Journal  of  Agricultural  Research, 
23:989-993.     1923. 


34  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

states  that  "an  increasing  amount  of  downy  mildew  has  developed 
particularly  since  the  variety  New  York  is  susceptible  to  that  disease. 
In  the  Imperial  Valley  the  disease  was  found  in  a  milder  form  than 
in  other  districts.  In  the  Los  Angeles  district,  the  fungus  was  found 
on  lettuce  during  all  months  of  the  year,  but  appeared  to  be  most 
active  from  October  to  May.  During  this  period,  in  many  fields  where 
the  plants  were  approaching  condition  for  harvest,  90  per  cent  of  the 
crop  was  affected  severely,  that  is  to  say,  the  fungus  was  found  on 
most  of  the  exposed  leaves  regardless  of  age.  In  a  survey  of  the 
whole  district  during  the  season  of  1919-20,  an  estimate  of  40  per 
cent  severe  infection  was  made.     In  the  Watsonville  and  Sacramento 


1  Lettuce    Heads   affected   with    Brown 
Blight.  Heads    all    same     age     and   m 
[growing    together    in     field 


Fig.    31. — Plant   on   left  normal,    others   are    affected    with    Brown    Blight. 

districts  the  severity  of  the  disease  was  similar  to  that  in  the  Los 
Angeles  district."  Downy  mildew  has  also  been  reported  in  the 
Colma  district. 

This  disease  is  important  because  it  attacks  the  edible  leaves  of  the 
plant  and  in  transit  predisposes  the  plant  tissue  to  slimy  soft  rot.  So 
far  no  methods  have  been  developed  for  its  control. 

Brown  Blight. — Dr.  I.  C.  Jagger,  Plant  Pathologist  of  the  United 
States  Department  of  Agriculture,  reports  that  the  Brown  Blight 
disease  has  caused  noticeable  injury  to  the  lettuce  crop  in  Imperial 
Valley.  It  has  also  been  found  recently  in  other  parts  of  the  state 
and  in  Arizona, 

Plants  are  attacked  by  the  disease  from  the  time  they  have  five 
or  six  leaves  until  their  heads  are  fully  matured.  Small  plants,  when 
attacked,  become  yellowish  in  color,  stop  growing,  and  fail  to  head. 
Such  plants  produce  a  few  small,  yellowish,  new  leaves,  which  lie  flat 
on  the  ground.  This  stunts  the  entire  plant,  as  shown  in  figure  31. 
Headed  or  partly  headed  plants  on  becoming  diseased  usually  show 


ClRC.  295]         GROWING  AND  HANDLING  LETTUCE  IN  CALIFORNIA 


35 


dark-brown,  dead,  irregular  blotches  and  streaks  in  the  leaves.  Begin- 
ning with  the  bottom  leaves,  the  affected  plants  turn  brown  and  wither. 
There  may  be  a  few  diseased  plants  scattered  throughout  the  field, 
or  there  may  be  smaller  spaces  in  which  all  or  a  large  percentage  of 
the  plants  are  diseased.  The  occurrence  of  the  disease  in  localized 
areas  is  often  noticeable,  and  has  frequently  led  to  the  erroneous  con- 
clusion that  it  is  associated  with  alkali  ' l  spots. "  In  severe  cases, 
entire  fields  may  have  from  50  to  90  per  cent  of  the  plants  affected. 


Fig.  32. — Field  of  lettuce  on  the  right  shows  from  75  to  100  per  cent  Brown 
Blight  infection.  Lettuce  was  grown  on  this  field  the  two  preceding  years.  The 
field  on  the  left  shows  from  20  to  40  per  cent  Brown  Blight  infection.  This  field 
produced  a  lettuce  crop  the  preceding  year.     Imperial  Valley. 

In  the  Imperial  Valley  the  disease  occurs  in  nearly  all  fields,  but 
in  general  it  causes  appreciable  injury  to  the  crop  only  where  lettuce 
is  grown  on  the  same  land  for  two  or  more  years.  (See  figure  32). 
Fields  growing  lettuce  for  the  first  time  often  have  from  2  to  5  per 
cent  of  the  plants  infected.  A  succeeding  crop  may  have  as  high  as 
50  per  cent  of  the  plant  diseases,  while  the  third  year  the  crop  may 
be  practically  a  total  failure.  Where  a  field  has  only  a  very  few 
diseased  plants,  a  good  crop  of  lettuce  can  usually  be  grown  on  the 
same-  land  the  following  year,  but  where  as  high  as  2  to  5  per  cent 
of  diseased  plants  are  present,  it  is  probable  that  lettuce  on  this  land 
the  following  year  will  have  from  15  to  50  per  cent  diseased. 

According  to  Jagger,  the  disease  is  caused  by  a  parasitic  organism, 
which  lives  in  the  soil.     So  far  as  known,  only  lettuce  is  susceptible. 


36  UNIVERSITY   OF    CALIFORNIA EXPERIMENT    STATION 

Information  on  the  effect  of  growing  other  crops  like  alfalfa  and  cotton 
for  a  few  years  on  infested  soil  is  limited,  but  in  general,  from  one 
to  three  years  of  such  crops  have  not  sufficiently  renovated  the  soil 
to  make  the  growing  of  lettuce  again  profitable. 

Some  varieties  are  entirely  immune  to  Brown  Blight,  but  these 
are  apparently  worthless  for  growing  in  California.  Very  satisfactory 
progress  is  being  made,  however,  in  developing  a  strain  of  the  New 
York  variety  which  is  immune  or  highly  resistant  to  the  disease,  and 
which  can  be  grown  on  infested  land.  Mr.  Jagger  expects  that  this 
resistant  strain  will  be  perfected  and  available  for  general  use  in  a 
few  years.  Meanwhile,  the  only  way  of  avoiding  losses  is  to  grow 
lettuce,  so  far  as  possible,  in  fields  which  are  reasonably  free  from 
infestation. 

SHOOTING   TO  SEED  PEEMATUEELY 

There  has  been  much  loss  during  the  past  three  or  more  years 
due  to  lettuce  plants  going  to  seed  prematurely.  This  may  in  some 
instance  be  due  to  poor  strains,  but  it  is  usually  caused  by  unfavorable 
soil,  moisture,  and  climatic  conditions.  It  is  difficult  to  determine 
in  all  cases  just  what  the  contributing  factor  or  factors  have  been 
in  bringing  about  this  condition.  Probably  one  of  the  most  general 
causes  is  insufficient  irrigation  during  periods  of  high  temperature 
or  when  dessicating  winds  are  prevalent.  Growers  who  do  not  permit 
the  growth  of  the  plants  to  become  checked  during  periods  of  adverse 
climatic  conditions  are  going  a  long  way  in  preventing  the  fields 
from  going  to  seed  prematurely.  The  best  lettuce  seed  available 
should  be  purchased.  Buying  cheap  seed  is  not  economy.  Above  all, 
growers  should  not  attempt  to  grow  lettuce  under  high  temperature 
conditions,  on  steep  slopes,  or  on  light  sandy  or  gravely  soils  that  are 
not  retentive  of  moisture. 

ACKNOWLEDGMENTS 

Many  thanks  are  due  Mr.  R.  G.  Risser,  Production  Manager  of 
the  California  Vegetable  Union  of  Los  Angeles  for  his  valuable  help 
and  many  excellent  suggestions,  and  for  the  certain  photographs  used. 
Mr.  Lester  L.  Morse  of  the  C.  C.  Morse  Seed  Company,  San  Fran- 
cisco, kindly  furnished  the  photograph  of  the  New  York  lettuce  plant. 
Mr.  F.  H.  Ernst,  Assistant  Farm  Advisor  of  Los  Angeles  County, 
supplied  a  photograph  and  Mr.  P.  S.  Williamson,  Assistant  Farm 
Advisor  of  Santa  Cruz  County,  supplied  photographs  for  two  figures. 
Photographs  for  two  figures  were  obtained  from  the  Los  Angeles 
Times. 


